40 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



limestones are persistent features of the upper beds of the Madison series 

 in this vicinity. These beds are overlain by the white Quadrant quartzites, 

 which are well exposed in the stream channel. In the bottom of the amphi- 

 theater at the head of Fawn Creek, a coarsely crystalline brown limestone 

 is well exposed. The rock is fossiliferous, but the fauna presents no features 

 different from those of the underlying limestones. The beds dip 10° N. 

 The amphitheater floor is heaped up in places with great piles of debris, 

 but presents many smooth exposures of a dark, slaty limestone and of the 

 coarsely crystalline rock just mentioned. In the latter there are nuineiwis 

 large sink holes or "swallow" 1 holes, in which the waters flowing from the 

 snow banks of the amphitheater walls pass underground, to reappear two 

 miles down the valley as a large stream which forms the headwaters of 

 Fawn Creek. The section of beds exposed in the amphitheater walls to 

 the east has already been given in the account of Quadrant Mountain. 

 Nowhere is the character of the Quadrant quartzite and of the immediately 

 underlying Madison limestones better shown than it is in the walls south of 

 Fawn Creek Valley. The sections which have already been given show 

 the relative thickness of these beds and the development of the impure 

 argillaceous dolomites whose red ledges form so prominent a feature of the 

 rock outcrops. 



A comparison of the sections of the Quadrant quartzites made on the 

 walls of Quadrant Mountain is given in the following table. A precise 

 separation of the sandstones from the interbedded limestones is not always 

 possible. Many of the sandstones are very calcareous, and in some cases 

 would perhaps be classed as arenaceous limestones. 



1 Handbook of Physical Geology, A.. J. Jukes-Brown, p. 87, London, 1884. 



